Top Line: Does daily, 10 fraction partial breast radiation result in toxicity and cosmesis similar to moderately hypofractionated whole breast radiation?
The Study: In the RAPID trial, 38.5 Gy accelerated partial breast irradiation (APBI) delivered in 10 BID fractions over 1 week resulted in comparable recurrence risk but increased late toxicity and adverse cosmesis compared to moderately hypofractionated whole breast radiation. In the post-game analysis, some felt that the twice daily treatment delivery may have resulted in a higher biologically effective dose to normal tissue and hence the adverse cosmetic effects. OPAL was a single-arm, phase 2 trial that sought to determine if 35 Gy in 10 daily fractions resulted in similar toxicity and cosmesis to a population of patients treated in a randomized trial of hypofractionated whole breast RT. Patients (n=149) were 50 or older and had unifocal in situ (20%) or invasive (80%), node negative breast cancer (pTis-2N0) breast cancer that was 3cm or less in size. Invasive disease also had to be hormone receptor positive. The CTV was a 2 cm expansion of the lumpectomy cavity minus chest wall bone/muscle and cropped 5 mm from the skin surface. A 5 mm PTV was used. Those with ≤2 mm margins (18%) received a 9 Gy in 3 fractions boost, and the boost CTV was a 1 cm expansion from the lumpectomy cavity. PBI planning goals required that 95% of the PTV receive 95% of Rx, 98% receive 98% of Rx, and the maximum dose to be ≤108%. 3D-CRT (79%), IMRT and VMAT could be used. The rate of grade 2+ toxicity over the 6 months following treatment was significantly lower than the historical control (17.4% v 72.7%). Across toxicity domains, PBI essentially shifted more patients to either no toxicity or grade 1 toxicity compared to WBRT. Patient reported cosmesis was similar to WBRT, but physician reported cosmesis was superior with PBI.
TBL: The phase 2 OPAL trial suggests 35 Gy in 10 fractions may be another safe and effective way to deliver partial breast radiation with less toxicity than whole breast RT. | Reddy, Int J Radiat Oncol Biol Phys 2022